When a high direct-current (DC) voltage is applied to a power cable according to the related art, a charge is injected from a conductor to an insulation layer or is easily formed in the insulation layer due to the influence of a cross linked byproduct of the insulation layer.
Space charges accumulated in the insulation layer distort an electric field of the cable and thus electric stress increases. Accordingly, the intensity of an electric field near the conductor increases and thus superimposed impulse breakdown strength decreases when impulse voltages overlap during application of DC voltage to the cable.
Conventionally, there has been disclosed a technique for reducing a space charge in an insulation layer of a power cable by trapping the space charge by adding inorganic particles to the insulation layer. However, the inorganic particles have a higher dielectric constant than that of polymer resin used to form the insulation layer. Accordingly, when the inorganic particles are added to the polymer resin of the insulation layer, a total dielectric constant of the insulation layer increases and thus impulse breakdown strength of the insulation layer decreases.
Accordingly, an insulation composition for increasing the lifespan of a cable by not only reducing a space charge in an insulation layer to improve superimposed impulse breakdown strength but also reducing a total dielectric constant to improve impulse breakdown strength of the insulation layer, and a cable including an insulation layer formed of the insulation composition are in urgent demand.